The trend coincides with a drop in violent crime in most major cities – something that also peaked in the early-to-mid-1990s, notes Drew DeSilver for the Pew Research “Fact Tank” blog. In 1991, according to Federal Bureau of Investigation data, there were about 758 violent crimes reported per 100,000 people. By 2012, the rate had fallen to about 387 crimes per 100,000 – the lowest rate in more than four decades.

Researchers have also pointed to more awareness of wrongful convictions as a factor in declining support for the death penalty, Mr. DeSilver says. He cites data from the National Registry of Exonerations, a joint project by the University of Michigan and Northwestern University law schools, that indicate 1,339 people have been exonerated since 1989 – including 106 who were sentenced to death.

DNA evidence played a role in less than a third of those exonerations, with perjured testimony, false accusations, and some form of official misconduct also factors.

Religious groups largely support the death penalty, but color makes a difference, Pew found. Sixty-seven percent of white evangelical Protestants, 64 percent of white mainline Protestants, and 59 percent of white Catholics support capital punishment – while only 33 percent of black Protestants and 37 percent of Hispanic Catholics do.

These findings line up with broader measures, Pew said. Sixty-three percent of white Americans support the death penalty, compared with 36 percent of blacks and 40 percent of Hispanics.

The number of executions each year has been dropping, according to data from the Death Penalty Information Center. In 1998, 98 people were executed; in 2013, 39 people were put to death. To date, 14 people have been executed this year.

One reason for the decline: state-issued moratoriums.

While the number of executions has been dropping in the US, it appears to be on the rise globally. Amnesty International released a report Thursday showing that execution by beheading, electrocution, firing squad, hanging, and lethal injection increased 15 percent in 2013 from the previous year.

China topped the list with 778 executions, followed by Iran (369), Iraq (169), Saudi Arabia (79), and the US (39). Texas accounts for the majority of executions in the US, with 40 percent of them.